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Solving Physical Science Word Problems: • Write down all given information • Write the formula you need to solve the problem. • Substitute the numbers in the equation. • Show all operations and solve. • Answers should include both numbers and units. • Circle the answer. Brandon pushes a 400 kg rock until it accelerates at the rate of 8 m/s2. What is the force required to produce this acceleration? • M = 400 kg • A = 8 m/s/s • F=M∙A • F = 400 kg ∙ 8 m/s/s • F = 3200 N Riley exerts a force • F→ = 150 N of 150 N on a 50 • M = 50 kg kg box. The box • If the box does not move, doesn’t move. F← = 150 N How much force does the box exert on Riley? A force of 25 N acts upon a 5 kg block. Calculate the acceleration. • F = 25N = 25 kg ∙m/s/s • M = 5 kg • A=F÷M • A = 25 ÷ 5 • A = 5 m/s/s An object of mass 45 kg is in free fall in a vacuum where there is no air resistance. Determine the acceleration of the object. • No air resistance means the object is in “free fall”. • Free fall means the only force acting on the object is the force of gravity (its weight). • The acceleration due to gravity is 9.8 m/s/s. Calculate the acceleration if. . . • Kiana pulls a 6 kg block pulled across a table with a force of 40 Newtons. A frictional force of 4 N opposes the motion. • F = 40 N → • F=4N← • Net Force = 40 N – 4 N = 36 N • • • • M = 6 kg A=F÷M A = 36 N ÷ 6 kg A = 6 m/s/s Tyler has a mass of • M = 65kg 65kg. What is • g = 9.8 m/s/s Tyler’s weight in Newtons? • Weight = m ∙ g In pounds? • Weight = 65 ∙ 9.8 • Weight = 637 N • 1 lb. = 4.4N • Weight = 637 /4.4 • Weight = 144.7 LBS. Now it’s your turn!!!! What is the force required for Marcus to throw a 15 kg ball up into the air at 3 m/s/s? • Marcus would first have to overcome the force of gravity on the ball… • Force of gravity on the ball= m ∙ g = 15 ∙ 9.8 m/s/s • F ↓ = 147 N • F ↑ = m ∙ a = 15kg ∙ 3m/s/s • F ↑ = 45 N • Total F needed to throw ball into the air = F↑ + F↓ = 45N + 147 N = 192N Josh, who has a mass of 80 kg, is extremely clumsy and fell out of an airplane during training. OH NO!!! He reaches terminal velocity before he can be rescued. What is the force of the air resistance? • Acceleration due to gravity = 9.8 m/s/s • M = 80 kg • Force of gravity = F↓ • F↓ = M ∙ g = 80 ∙ 9.8 • F↓ = 784 N • Air Resistance = F↑ • Terminal Velocity occurs when force of gravity = air resistance (F↑ = F↓) • F↑ = 784 N An object with a mass of 30 kg is falling in air and experiences a force due to air resistance of 50 newtons. A = F ÷ M, But first you have to calculate the net force. • • • • • • M = 30 kg F↑ (air resistance) = 50 N F ↓ = weight Weight = m ∙ g Weight = 30 kg ∙ 9.8 m/s/s Weight = 294 N • Net Force = Weight – Air Resistance • Net Force = F ↓ - F↑ • Net Force = 294 N – 50 N • Net Force = 244 N An object with a mass of 30 kg is falling in air and experiences a force due to air resistance of 50 Newtons. • A=F÷M • A = 244 N ÷ 30 kg • A = 8.13 m/s/s A 40 kg cannon is pushed with a force of 200 N. What is its acceleration? If you put a 40 kg cannonball into the cannon and push it with the same force, how much does it accelerate? • • • • M = 40 kg F→ = 200N A = F ÷ M = 200 ÷ 40 A = 5 m/s/s • • • • M = 40kg + 40Kg = 80kg F→ = 200N A = F ÷ M = 200 ÷ 80 A = 2.5 m/s/s Now it’s your turn!!!!